Parametric Reconstruction of Audio Signals

1. A method of reconstructing an N-channel audio signal (X) based on a single-channel downmix signal (Y), the method comprising: receiving, by a decorrelating section of a parametric reconstruction system, the single-channel downmix signal (Y); processing the single-channel downmix signal (Y) to output an (N−1)-channel decorrelated signal (Z), the processing including applying respective filters to the single-channel downmix signal (Y); receiving, by a dry upmix section of the parametric reconstruction system, the single-channel downmix signal (Y) and dry upmix parameters ({tilde over (C)}), the dry upmix parameters ({tilde over (C)}) coinciding with a first portion of a set of dry upmix coefficients (C); determining a second portion of the set of dry upmix coefficients (C) based on a predefined relation between the set of dry upmix coefficients (C); outputting, by the dry upmix section, a dry upmix signal (CY) computed by mapping the single-channel downmix signal (Y) linearly in accordance with the set of dry upmix coefficients (C); receiving, by a wet upmix section of the parametric reconstruction system, the (N−1)-channel decorrelated signal (Z) and a set of wet upmix parameters (({tilde over (P)}); deriving, from the set of wet upmix parameters (({tilde over (P)}), a set of wet upmix coefficients (P); outputting, by the wet upmix section, a wet upmix signal (PZ) computed by mapping the (N−1)-channel decorrelated signal (Z) and the set of wet upmix coefficients (P); and combining, by a combining section of the parametric reconstruction system, the dry upmix signal (CY) and the wet upmix signal (PZ) to obtain a multidimensional reconstructed signal ({circumflex over (X)}) corresponding to the N-channel audio signal (X) to be reconstructed, wherein the parametric reconstruction system includes one or more processors.

2. The method of claim 1 , comprising: populating an intermediate matrix having more elements than the number of received wet upmix parameters, based on the received wet upmix parameters, the intermediate matrix belonging to a predefined matrix class.

3. The method of claim 2 , wherein deriving the set of wet upmix coefficients comprises multiplying the intermediate matrix by a predefined matrix, wherein the set of wet upmix coefficients corresponds to a matrix resulting from the multiplication and includes more coefficients than the number of elements in the intermediate matrix.

4. The method of claim 3 , wherein the predefined matrix class is one of: lower or upper triangular matrices with predefined matrix elements being zero; symmetric matrices with predefined matrix elements being equal; and products of an orthogonal matrix and a diagonal matrix with known relations between predefined matrix elements.

5. The method of claim 3 , wherein the wet upmix parameters include N(N−1)/2 wet upmix parameters, wherein populating the intermediate matrix includes obtaining values for (N−1) 2 matrix elements based on the N(N−1)/2 wet upmix parameters and knowing that the intermediate matrix belongs to the predefined matrix class, wherein the predefined matrix includes N(N−1) elements, and wherein the set of wet upmix coefficients includes N(N−1) coefficients.

6. The method of claim 2 , wherein populating the intermediate matrix includes employing the received wet upmix parameters as elements in the intermediate matrix.

7. An audio decoding system comprising a first parametric reconstruction section configured to reconstruct an N-channel audio signal (X) based on a first single-channel downmix signal (Y), the audio decoding system comprising: a first decorrelating section of a parametric reconstruction system configured to perform operations comprising: receiving the single-channel downmix signal (Y); processing the single-channel downmix signal (Y), the processing including applying respective filters to the single-channel downmix signal (Y); and output an (N−1)-channel decorrelated signal (Z); a first dry upmix section configured to perform operations comprising: receiving the single-channel downmix signal (Y) and dry upmix parameters ({tilde over (C)}), the dry upmix parameters ({tilde over (C)}) coinciding with a first portion of a set of dry upmix coefficients (C); determining a second portion of the set of dry upmix coefficients (C) based on a predefined relation between the set of dry upmix coefficients (C); and outputting a dry upmix signal (CY) computed by mapping the single-channel downmix signal (Y) linearly in accordance with the set of dry upmix coefficients (C); a first wet upmix section of the parametric reconstruction system configured to perform operations comprising: receiving the (N-1)-channel decorrelated signal (Z) and a set of wet upmix parameters (({tilde over (P)}); deriving, from the set of wet upmix parameters ({tilde over (P)}), a set of wet upmix coefficients (P); and outputting a wet upmix signal (PZ) computed by mapping the (N−1)-channel decorrelated signal (Z) and the set of wet upmix coefficients (P); and a combining section configured to perform operations comprising: combining the dry upmix signal (CY) and the wet upmix signal (PZ) to obtain a multidimensional reconstructed signal ({circumflex over (X)}) corresponding to the N-channel audio signal to be reconstructed, wherein the first parametric reconstruction section includes one or more processors.

8. The system of claim 7 , wherein the first parametric reconstruction section is configured to perform operations comprising: populating an intermediate matrix having more elements than the number of received wet upmix parameters, based on the received wet upmix parameters, the intermediate matrix belonging to a predefined matrix class.

9. The system of claim 8 , wherein deriving the set of wet upmix coefficients comprises multiplying the intermediate matrix by a predefined matrix, wherein the set of wet upmix coefficients corresponds to a matrix resulting from the multiplication and includes more coefficients than the number of elements in the intermediate matrix.

10. The system of claim 9 , wherein the predefined matrix class is one of: lower or upper triangular matrices with predefined matrix elements being zero; symmetric matrices with predefined matrix elements being equal; and products of an orthogonal matrix and a diagonal matrix with known relations between predefined matrix elements.

11. The system of claim 9 , wherein the wet upmix parameters include N(N−1)/2 wet upmix parameters, wherein populating the intermediate matrix includes obtaining values for (N−1) 2 matrix elements based on the N(N−1)/2 wet upmix parameters and knowing that the intermediate matrix belongs to the predefined matrix class, wherein the predefined matrix includes N(N−1) elements, and wherein the set of wet upmix coefficients includes N(N−1) coefficients.

12. The system of claim 8 , wherein populating the intermediate matrix includes employing the received wet upmix parameters as elements in the intermediate matrix.

13. A non-transitory computer-readable medium storing instructions that, when executed by one or more processors, cause the one or more processors to perform operations of reconstructing an N-channel audio signal (X) based on a single-channel downmix signal (Y), the operations comprising: receiving, by a decorrelating section of a parametric reconstruction system, the single-channel downmix signal (Y); processing the single-channel downmix signal (Y) to output an (N−1)-channel decorrelated signal (Z), the processing including applying respective filters to the single-channel downmix signal (Y); receiving, by a dry upmix section of the parametric reconstruction system, the single-channel downmix signal (Y) and dry upmix parameters ({tilde over (C)}), the dry upmix parameters ({tilde over (C)}) coinciding with a first portion of a set of dry upmix coefficients (C); determining a second portion of the set of dry upmix coefficients (C) based on a predefined relation between the set of dry upmix coefficients (C); outputting, by the dry upmix section, a dry upmix signal (CY) computed by mapping the single-channel downmix signal (Y) linearly in accordance with the set of dry upmix coefficients (C); receiving, by a wet upmix section of the parametric reconstruction system, the (N−1)-channel decorrelated signal (Z) and a set of wet upmix parameters (({tilde over (P)}); deriving, from the set of wet upmix parameters (({tilde over (P)}), a set of wet upmix coefficients (P); outputting, by the wet upmix section, a wet upmix signal (PZ) computed by mapping the (N−1)-channel decorrelated signal (Z) and the set of wet upmix coefficients (P); and combining, by a combining section of the parametric reconstruction system, the dry upmix signal (CY) and the wet upmix signal (PZ) to obtain a multidimensional reconstructed signal ({circumflex over (X)}) corresponding to the N-channel audio signal (X) to be reconstructed.